Bake a sheet cake the size that you need.
Ice the cake with white icing using a cake spatula and
making sure the surface is smooth.
Using parchment paper, cut a piece that is as big as the cake top.
Cut a rectangle out of the center the size that you want the rainbow to be.
Place the parchment paper frame on the ballerina cake top.
With food color sprays (also known as color mist),Spray strips of rainbow in the center that you cut out from the parchment paper.
Lift the parchment border off.
On the remaining white top edge and sides of the cake do lace work using round tip, size #5 and white icing.
With star tip, size #18, make a shell border along the inside and outside edge of the lace work border and the bottom edge of the sides of the cake.
I bought a mall china doll and placed her on the cake top burying the base of the ballerina doll stand in the cake. These dolls can be purchased in most craft stores.
With round tip, size #15, write the birthday message on the cake board in white icing.